Bacteriostatic Water for Peptides: What It Is and Why It Matters
Bacteriostatic water is the standard diluent for reconstituting research peptides — but it is easy to confuse with other "waters." Here is what it is, why the difference matters, and how to use it.
What bacteriostatic water is
Bacteriostatic water is sterile water that contains 0.9% benzyl alcohol as a preservative. The benzyl alcohol is "bacteriostatic" — it inhibits the growth of bacteria — which is what lets a reconstituted vial be entered and drawn from multiple times over a period of days to weeks.
How it differs from sterile water
Plain sterile water (or sterile water for injection) has no preservative. Once you pierce the stopper, there is nothing stopping microbial growth, so it is really intended for single use. Bacteriostatic water's preservative is exactly what makes multi-draw research vials practical.
Tap water and distilled water are not sterile and should never be used to reconstitute a peptide.
Why the benzyl alcohol matters
Beyond inhibiting bacteria, the small amount of benzyl alcohol keeps a multi-use vial usable across its refrigerated life. This is why most reconstitution references and calculators assume bacteriostatic water rather than plain sterile water.
How much to use
That depends on the concentration you want, not on a fixed rule. More water = a more dilute, larger, easier-to-read draw; less water = a more concentrated, smaller draw. A reconstitution calculator turns your vial size and chosen water volume into an exact syringe draw so you can pick sensibly.
Storage
Keep bacteriostatic water at room temperature or refrigerated, out of direct light, and note that once opened it has a limited usable window (often cited around 28 days). Wipe the stopper with alcohol before each draw.
Key takeaways
- Bacteriostatic water = sterile water + 0.9% benzyl alcohol (a preservative).
- The preservative is what makes multi-draw vials possible — plain sterile water is single-use.
- Never use tap or distilled water to reconstitute peptides.
- How much to add depends on the concentration you want — let the calculator decide.
